The present invention relates to copolymers of ethylene with xcex1-olefins and to the process for their preparation. More particularly, the present invention relates to substantially amorphous copolymers of ethylene with one or more xcex1-olefins containing 4 or more carbon atoms, and optionally with a minor amount of polyenes.
Copolymers of ethylene with one or more xcex1-olefins and optionally a minor amount of polyenes are known which, after vulcanization, exhibit elastomeric type properties. The most common of these are copolymers of ethylene with propylene (EPR), which can contain small amounts of non-conjugated diene monomers (EPDM).
Thanks to their good resistance to high temperatures, chemical and atmospheric agents, and their dielectric properties, these elastomers find uses in various application fields. Principally they can be used as additives for lubricating oils, covering materials in building, electric insulators, components in the automotive industry or modifiers in mixtures with thermoplastic polymers.
Elastomeric copolymers of ethylene with xcex1-olefins different from propylene, at the date of the present invention, do not have interesting industrial application.
The above mentioned ethylene copolymers are generally prepared in the presence of Ziegler-Natta catalysts.
Natta et al, for example, in xe2x80x9cLa Chimica e l""Industria, 41, 769 (1959)xe2x80x9d, describe copolymerization reactions of ethylene with 1-butene in the presence of vanadium halides and trialkyl aluminium compounds.
The copolymers so obtained have a high tendency to produce blocks of xcex1-olefin comonomers in the chain, and this gives rise to crystallinity negatively influencing the final characteristic of the product. Therefore, in order to obtain vulcanized copolymers which are endowed with good elastomeric properties, it is important that the distribution of the monomeric units within the chain is as homogenous as possible.
Zambelli et al., in xe2x80x9cMakromol. Chem., 115, 73 (1968)xe2x80x9d describe the preparation of copolymers of ethylene and 1-butene in the presence of a catalytic system comprising VCl4, AlEt2Cl and anisole. The copolymers obtained have a tendency to an alternating distribution of the comonomer.
More recently, ethylene copolymers of this type have been prepared in the presence of homogeneous catalysts obtained from metallocenes and aluminoxane compounds.
U.S. Pat. No. 5,001,205, for example, describes a process for the preparation of elastomeric copolymers of ethylene with xcex1-olefins, in which the product obtained from the reaction of methylaluminoxans (MAO) with a bis-cyclopentadiene compound of Zr, Ti, or Hf, such as bis(tetrahydroindenyl)zirconium dichloride, ethylene-bis(tetrahydroindenyl)zirconium dichloride, or dimethylsilandiyl-bis(tetrahydroindenyl)zirconium dichloride, is used as a catalyst. The working examples only regard ethylene/propylene copolymers.
The homogeneity of the distribution of the xcex1-olefin monomeric units in the copolymers obtained operating in the presence of these types of catalyst, although turning out improved with respect to the copolymers obtained from Ziegler-Natta catalysts, is still not totally satisfactory.
Hence, it would be extremely advantageous to obtain copolymers of ethylene with xcex1-olefins different from propylene, and optionally with minor amounts of polyenes, in which the homogeneity of the distribution of the xcex1-olefin monomeric units is sensibly improved.
It has been unexpectedly found that, by carrying out the polymerization reaction in the presence of particular metallocene catalysts, it is possible to prepare ethylene/xcex1-olefin copolymers or ethylene/xcex1-olefin/diene terpolymers in which the distribution of comonomers in the polymeric chain is extremely homogeneous.
It is therefore an object of the present invention a substantially amorphous copolymer of ethylene with one or more xcex1-olefins of formula (I):
CH2xe2x95x90CHRxe2x80x83xe2x80x83(I)
wherein R is an alkyl radical having from 2 to 10 carbon atoms, and optionally with one or more polyenes, having a content of ethylene derived units comprised between about 35% and 85% by mole, a content of xcex1-olefin derived units comprised between about 10% and 60% by mole and a content of polyene derived units comprised between about 0 to 5% by mole, and having the following characteristics:
(A) the % by mole content of xcex1-olefin in the copolymer (%xcex1) and the ratio between the molar amount of xcex1-olefin diads and the molar content of xcex1-olefin in the copolymer (xcex1xcex1/xcex1) satisfy the following relationship:
(%xcex1)xe2x88x92250(xcex1xcex1/xcex1)xe2x89xa710
(B) less than 2% of the CH2 groups in the polymeric chain are in sequences (CH2)n, wherein n is an even number.
Another object of the present invention is an elastomeric copolymer obtainable by subjecting the above said copolymer to a vulcanization process.
Still another object of the present invention is a shaped article obtained from an elastomeric copolymer according to the invention.
A further object of the present invention is a process for the preparation of the above said substantially amorphous copolymers of ethylene.
The content by mole of ethylene derived units is preferably comprised between about 50% and 85% and more preferably between about 60% and 80%.
The molar content of xcex1-olefin derived units is preferably comprised between about 15% and 50% and, more preferably, between about 20% and 40%.
The content of polyene derived units is preferably comprised between about 0 and 4% and, more preferably, between about 0 and 3%.
Non-limitative examples of xcex1-olefins which can be used as comonomers in the copolymers according to the present invention are 1-butene, 1-hexene, 4-methyl-1-pentene, 1-octene and 1-decene.
The polyenes which can be used as comonomers in the copolymer of the invention are comprised in the following classes:
non-conjugated diolefins capable of cyclopolymerization such as, for example, 1,5-hexadiene, 1,6-heptadiene, 2-methyl-1,5-hexadiene;
dienes capable of giving unsaturated monomeric units, in particular conjugated dienes such as, for example, butadiene and isoprene, and linear non-conjugated dienes such as, for example, trans 1,4-hexadiene, cis 1,4-hexadiene, 6-methyl-1,5-heptadiene, 3,7-dimethyl-1,6-octadiene, 11-methyl-1,10-dodecadiene.
A particularly interesting embodiment of the present invention is constituted of substantially amorphous copolymers of ethylene with 1-butene.
The copolymers according to the present invention are substantially void of crystallinity. Their melting enthalpy (xcex94Hf) are lower than about 20 J/g and, preferably, lower than about 10 J/g. With the exception of the copolymers in which the amount of ethylene derived units is close to the upper limit of 85% molar, the copolymers according to the invention generally have a melting enthalpy of 0 J/g.
The copolymers according to the invention are characterised by an extremely homogenous distribution of the comonomers in the polymeric chain and, more precisely, by the fact of containing a number of sequences of two or more consecutive units of the xcex1-olefin derived units which is extremely low, and anyway lower than in the copolymers known at the date of the present invention.
The analysis of the distribution of the xcex1-olefin in the copolymers of the invention has been carried out using 13C-N.M.R. The assignments, in the case of ethylene/1-butene copolymers, were carried out as described by J. C. Randall in xe2x80x9cMacromolecules (1982), 15, 353-360xe2x80x9d.
The spectra are divided in the following eight areas:
(A1) from 40.0 to 38.9 ppm,
(A2) 37.2 ppm,
(A3) from 34.8 to 34.16 ppm,
(A4) from 34.16 to 33.5 ppm,
(A5) from 31.0 to 29.0 ppm,
(A6) from 27.5 to 26.8 ppm,
(A7) from 26.8 to 26.5 ppm,
(A8) from 25.0 to 24.0 ppm.
The concentration (molar fraction) of the diads is obtained from the following equations:
EE=0.5[A5+0,5(A6xe2x88x92A2) ]/Z
EB=0.5[A1+A3+A4+0,5(A6xe2x88x92A2)+A8]/Z
BB=0.5(A2/Z)
with Z=EE+EB+BB, wherein EE, EB and BB represent the sequences ethylene/ethylene, ethylene/1-butene and 1-butene/1-butene in the copolymer respectively.
The number of xcex1-olefin sequences results to be dependent on the amount of xcex1-olefin monomeric units present in the chain.
In particular, the % content by mole of xcex1-olefins in the copolymer (%xcex1) and the % content by mole of xcex1-olefin diads (%xcex1xcex1) satisfies the following relationship:
(%xcex1)xe2x88x929 (%xcex1xcex1)xe2x89xa710
preferably:
(%xcex1)xe2x88x9210(%xcex1xcex1)xe2x89xa710
more preferably:
xe2x80x83(%xcex1)xe2x88x9211(%xcex1xcex1)xe2x89xa710
If the ratio between the amount by mole of xcex1-olefin diads and the content by mole of xcex1-olefins in the copolymer (xcex1xcex1/xcex1) is considered, the copolymers of the invention satisfy the following relationship:
(%xcex1)xe2x88x92250(xcex1xcex1/xcex1)xe2x89xa710
preferably:
(%xcex1)xe2x88x92300(xcex1xcex1/xcex1)xe2x89xa710
more preferably:
(%xcex1)xe2x88x92350(xcex1xcex1/xcex1)xe2x89xa710